Galileo Mission Status - January 13, 1998
MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 http://www.jpl.nasa.gov
Members of the Galileo flight team are busy studying data on two incidents of anomalous behavior that have occurred, one during the spacecraft's December 16, 1997 flyby of Europa, and one since. In both cases, the anomalies involved the attitude control subsystem, which controls where the spacecraft and scan platform are pointing. Team members believe the culprit may be one of the spacecraft's two gyroscopes. The gyroscopes are used to point the spacecraft when there is a need for very precise pointing control and knowledge of the spacecraft, usually for remote sensing science observations or orbit trim maneuvers.
Although the anomalies are not considered serious, until the situation was corrected, Galileo's radio antenna was pointing in a direction about 10 degrees from Earth, about eight degrees greater than the normal attitude for ideal transmission of information to Earth. Nonetheless, Galileo was still able to transmit pictures and other information stored on its tape recorder during the Europa flyby, but the data was sent at a lower rate to compensate for the large angle.
To help correct the spacecraft's attitude and speed up the data transmission, the Galileo team reduced the angle between Earth and the radio antenna by performing a Sun acquisition turn, which turned the spacecraft toward the Sun by using the Sun's bright light as a guide. This turn, which was performed Sunday night, means that the antenna is now about 3.1 degrees from Earth. The spacecraft is now operating normally, but the cause of the anomalies is still not fully understood, and the team is continuing its investigation.
This week, Galileo is expected to transmit to Earth high time resolution fields and particles information on the interaction between Europa and the magnetic and electric field environment of Jupiter. Also on the playback schedule are images of Europa's Conamara Chaos region, an area of bright, icy crust that has broken apart, exposing darker underlying material. There may be some pictures of Europa's regions of mottled or "blotchy" terrain.
Scientists are particularly interested in seeing the pictures taken by Europa during the December 16 encounter, because the flyby was the closest ever to be performed by Galileo, with the spacecraft dipping down to 200 kilometers (124 miles) above the icy moon's surface.
The spacecraft recently began a two-year extended mission, known as the Galileo Europa Mission, which will include a total of eight Europa flybys, four of Callisto, and one or two of Io, as long as the spacecraft remains healthy.
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